1. Field of the Invention
The present invention generally relates to a navigation apparatus and a navigation method, and more particularly to a navigation apparatus and a navigation method in which a route guidance is performed by use of route data set in advance.
2. Description of the Related Art
There is a so-called "built-in type navigation apparatus" as a measuring apparatus for various movable bodies such as a vehicle, an aeroplane, a ship etc.. This built-in type navigation apparatus is constructed to obtain a two dimensional displacement (i.e. a vector amount) of the movable body from an azimuth data of an azimuth sensor and a speed data of a speed sensor and obtain a present position by integrating this two dimensional displacement on a standard point. Namely, in case of an automobile for example, it is constructed such that the number of pulses which are generated during one rotation of a drive shaft is set in advance, and that the travel distance is obtained by multiplying a distance, which is calculated from the total number of the pulses generated from the standard point to the present position, by a distance correction coefficient.
There is also a GPS (Global Positioning System) type navigation apparatus as a measuring apparatus, which utilizes artificial satellites. This GPS type navigation apparatus is constructed as following. Namely, it receives electric waves of three or more GPS satellites normally, and calculates a present position of a receiving point from the pseudo-distance data, which include a time offset of a receiver between each GPS satellite and the receiving point and the positional data of each GPS satellite. Then, an information processing device reads out map data, which include the calculated present position, from a map data storing device, to take in the data. Then, the information processing device forms image data from the taken-in map data and the information of the present position, and sends it to the display device to perform the image display. By this image, the automobile driver etc. who is a user can recognize the self present position in relation with the map.
Both of the above mentioned navigation apparatuses are constructed to allow the user to visually recognize the present position and the objective position by sight by overlapping them on the map on the picture plane of the display apparatus.
In the above explained navigation apparatuses, the following operations are performed, for example.
Now, a self vehicle which is the movable body is assumed to travel from a start position P0' to a final destination Pn'.
When the self vehicle position is located at the start position PO', if the operator gives the navigation apparatus an instruction to set the route positions automatically, the navigation apparatus calculates the scheduled route positions P1', P2', P3',..., Pn' along the route in this order on the basis of an algorithm set in advance.
Then, when the calculation of the scheduled route positions is finished, the navigation apparatus outputs a message to perform the route guidance on the basis of the scheduled route positions form the obtained scheduled route position P1' to the scheduled route position Pn' in the order.
In the above explained navigation apparatus, even if the self vehicle position has already passed through several route positions at the time of searching e.g. if the self vehicle is travelling while searching the route, the message is outputted such that the scheduled route position P1', which the self vehicle should firstly pass through, is still treated as the objective route position.
Thus, if the self vehicle has already passed through the scheduled route positions P1', P2' and P3' at the timing when it is ended to set up the scheduled route positions, the navigation apparatus outputs such a message that the next objective route position is the position P1' although it has in fact already passed through the scheduled route positions P1', P2' and P3'.
Therefore, there is a problem that, when such an erroneous message is outputted, the self vehicle may be guided in an incorrect direction, or the operator should perform an operation to cancel the message etc. if he recognizes the fact that it has already passed the pertinent position, and thus the operatability is degraded.